Always remember that it is intended that you don't see the same face so you have to work on it a bit. A little effort will pay off big. In those three frames the easiest facial feature to compare are the mouths and teeth. This isn't the easiest example to see. Every time you look at a picture or TV or a movie practice comparing facial features. TV commercials in general are easier to see than most of what is ontv. Low budget movies usually don't do as good a job of fooing us. But overall the easiest place to see this is anything directed at kids. They can get sloppy there. Still pictures are easiest to compare so when you pick up a movie look at the pictures on the cover.
When you spend time comparing facial features it trains your eye to look at detail and to look at what is the same not just what is different.